1. Field of the Invention
The present invention relates to a method of determining a set value for a side trimming machine to trim a width of an elongate workpiece such as an uncoiled hoop or a steel strip.
2. Description of the Prior Art
It has been customary to determine a set value for such a side trimmer on the basis of two different data, i.e. an actual width of the hoop produced in a rolling mill upstream of the side trimmer and a final width which a finally trimmed hoop or product will have. For this purpose there are provided a measuring unit for measuring the hoop produced in the rolling mill to obtain an actual width thereof and a recorder unit for recording the values thus obtained, these two units being disposed upstream of the side trimmer. The hoop is continuously measured in width as it advances from its leading end to its trailing end and then the values thus measured are recorded as in a chart, an example of which is shown in FIG. 1 of the accompanying drawings (as described later on).
Then a final set width W2 of the product or finished hoop is determined on the basis of the data of the width thus obtained, including an actual minimum width W1 of the hoop. In obtaining the final set width W2, a total trimming allowance value, i.e. the difference between the minimum width W1 of the untrimmed hoop and the final set width W2 of the trimmed hoop, which is represented by W1-W2, is determined. The minimum width W1 thus obtained, however, is based on an edge-to-edge measurement data, but not on an edge-to-center measurement data including minimum widths of adjacent side portions disposed at both sides of a reference line on the hoop. Thus in such prior practice, the total trimming allowance value is usually set to be large enough to avoid a mistrimming due to insufficiency of the allowance.
With the set values thus determined, the side trimmer cuts off opposite side edge portions of the hoop by a value equal to a half of the total trimming allowance, i.e. 1/2(W1-W2). The hoop is customarily coiled upstream of the side trimming station because of necessity of transportation between the rolling mill and the side trimmer which are not linearly continuously connected to each other. Subsequently, the hoop in coil form must be uncoiled to be trimmed at the opposite side edges in the side trimmer.
According to the conventional practice, a set value for the side trimmer is determined on the basis of the total trimming allowance equal to difference between the actual width of the hoop and the final width thereof as shown in FIG. 2, in which respective trimming allowance values of the opposite side stock portions of the hoop, i.e. a work side portion and a drive side portion are artificially considered as equal. However, if dimensional variations in the respective widths of the work side and drive side portions are very large, either of a pair of trim lines or final edge lines of the product can fail to be located within the work side portion or the drive side portion due to the insufficiency of the trimming allowance, thus causing a mistrimming. To increase the total trimming allowance for prevention of such mistrimming is disadvantageous in view of consumption of the material.